Various fixes

This PR fixes a critical bug created by https://github.com/ElementalAlchemist/txircd/pull/9 that caused txircd to not start anymore, as it was trying to initialize a `LoopingCall` while the `storage` was still `None`.

Another thing fixed by this PR is the sending of RPL_YOUREOPER after a successful oper attempt. This is currently missing, which is in violation of the RFC. I also implemented an error sent to the user when they try to manually set umode +o.